In many generators, such as high speed generators utilized in aircraft, it is highly desirable to eliminate brushes since they frequently require maintenance and/or replacement, and are perhaps the single weakest point in the system in terms of breakdowns. Moreover, by its very nature, the electrical path between a brush and a commutator is subject to arcing which may introduce transients into the electrical energy being produced, which in turn, may interfere with proper operation of some types of electrical loads on the generator.
A typical brushless generator has three distinct generating systems including a main generator, an exciter, and a permanent magnet generator. The permanent magnet generator includes permanent magnets for establishing a magnetic field which is electrically employed to induce current in a set of windings, which in turn is employed after rectification to generate a magnetic field in the exciter. The magnetic field in the exciter is in turn employed to induce an even higher level of current, typically three-phase alternating current, which is then employed after rectification to generate the magnetic field for the main generator by flowing the DC current through the main field winding of the main generator.
In order to avoid the use of brushes, it is necessary that the magnetic field in the main generator be in the rotor so that the output of the system can be taken from the stator of the main generator. In order to generate a suitable magnetic field in the rotor, it is necessary to utilize direct current, as opposed to alternating current, for the same. Since the output of the exciter is an alternating current, this current must be rectified by a rectifier assembly to direct current. And, again, in order to avoid resort to brushes, it is accordingly necessary that the rectifier assembly interconnecting the exciter and the main generator field winding be carried by the rotor of the generator.
Such a rectifier assembly should also be capable of withstanding high centrifugal loading. Further, it should be easily removable for servicing in the event of component failure.
One such rectifier assembly is disclosed in commonly owned U.S. Pat. No. 4,628,219, issued Dec. 9, 1986 to Troscinski, the details of which are herein incorporated by reference. The Troscinski structure is intended for installation in a generator system wherein the generator shaft is supported by bearings. Exciter leads couple the exciter to the rectifier assembly. Further, the shaft has an opening in it between the rectifier assembly and the bearing through which the exciter leads pass from the rectifier assembly to the exciter. Accordingly, the exciter leads do not pass under the bearing. To remove the rectifier assembly from the rotor, one simply detaches the exciter leads from the rectifier assembly and pulls the exciter leads from the exciter through the opening and away from the path of removal of the rectifier assembly.
However, according to another rotor design, a Troscinski rectifier assembly will extend under the bearing. The exciter leads must pass under the bearing to couple to the exciter. Because of the resulting interference with the bearing, the exciter leads cannot be pulled away from the path of removal of the rectifier assembly. The exciter leads remain stationary and interfere with the installation and removal of the rectifier assembly. To install or remove the rectifier assembly, the bearing and rotor balance ring must first be removed.
The present invention is directed to overcoming one or more of the above problems.